EP2936666B1 - Electric machine with superconductive windings - Google Patents

Description

The present invention belongs to the field of electromechanical machines, motors or generators, the coils of which in operation are maintained at very low temperatures.

More particularly, the invention relates to an electromechanical machine in which the temperatures of the windings of the coils are maintained at temperatures low enough to ensure the superconducting operation of these coils.

Electrical superconductivity is a well-known phenomenon that originates in certain materials and makes their electrical resistivity practically zero.

This property of certain materials is particularly advantageous because it results in the possibility of producing windings to generate magnetic fields that can accept large electric currents, provided that certain critical current densities are not exceeded, without heating by the Joule effect and with conductive sections, and therefore the masses of the windings, reduced.

In return, it is necessary to obtain this behavior of the material to maintain it at temperatures below a critical temperature, depending on the conductive material used, temperatures that can be cryogenic and close to absolute zero, at least for certain modes. of superconductivity.

This constraint has been the cause of a development of superconducting coil machines limited to static applications such as coils used in particle accelerators or in magnetic resonance imaging devices, and more recently for the storage of energy in magnetic form, for which permanent cooling necessary could without insurmountable inconvenience be achieved by heavy and complex installations to implement.

The discovery of so-called "high temperature" superconducting materials, for example magnesium diboride MgB2 whose superconductivity is obtained for temperatures of the order of 30 Kelvin or other alloys which can exhibit superconductivity for temperatures as high as 70 Kelvin, reduces temperature constraints and simplifies the cooling systems of machines using superconducting coils.

The European patent application published under number EP 1777800 describes an example of an electromechanical machine using a superconducting winding.

In this example, the superconducting winding, located between the rotor and the stator, is enclosed in a cryostat placed inside the machine so that the winding is maintained at a temperature below the critical temperature of the material used. There is no explanation of how the cryostat is maintained at the desired temperature.

In known manner, such maintenance at low temperature is obtained by a fluid such as for example liquid nitrogen or helium or liquid hydrogen, depending on the critical temperature of the superconducting material used, maintained at the desired temperature by cooling systems.

In a first known method, a tank of liquefied gas at low temperature is used as a cold reserve and a flow is taken from this tank to permanently cool the electric conductors made of superconducting material of the machine before being discharged outside. of the machine.

In this case it is necessary to provide a sufficient mass of gas liquefied at cryogenic temperature, storage means allowing this gas to be maintained at its liquefaction temperature and regulation means for distributing the gas so as to maintain the superconducting elements of the machine at the desired temperature while minimizing gas consumption.

When the machine is on board a vehicle, in addition to the penalizing need to carry a sufficient quantity of gas, it is necessary to provide distribution and regulation means whose operation at cryogenic temperature is more complex than in the case of systems operating at room temperature.

In a second known method, a low-temperature fluid circulates in a closed circuit between the parts of the machine to be maintained at cryogenic temperature and a device for generating cryogenic cold (cryocooler in Anglo-Saxon terminology).

Such devices for generating cryogenic cold are known but they remain heavy and bulky and require to be supplied with energy to produce the necessary cold.

In the case of the use of such devices, a failure of the cooling system generally has the immediate consequence of stopping the operation of the cooled machine unless provision is made for redundant cooling devices.

The document DE19710501 describes an electric machine comprising a stator generating a rotating magnetic field to drive a rotor mounted on a shaft of the machine. The outer part of the rotor is formed of a high temperature superconducting material, cooled to low temperature via a cooling device.

The document US2010/164309 discloses a superconducting motor apparatus whose superconducting motor comprises a superconducting coil and a moving motor based on a moving magnetic field generated by the superconducting coil when electric power is supplied thereto. The motor further includes a container defining an outer vacuum thermal insulation chamber that covers an outer chamber and an extremely low temperature generating portion cooling the superconducting coil of the superconducting motor to a temperature equal to or below a critical temperature of the coil superconductive.

The document "Magnetiche Charakterisierung von schmelztexturierten YBa CU O ₇ , Hochtemperatur-Supraleitern describes applications of the material YBa Cu superconductor

O ₇ including a linear guide implementing the superconducting material. In the proposed experimental setup, the superconducting material is immersed in an insulated tank filled with nitrogen so that the device operates until the liquid nitrogen evaporates.

The known methods therefore prove to be penalizing and are not satisfactory for on-board machines when in particular the volume, the mass and the reliability are essential criteria as for example in the case of applications on board aircraft.

The invention provides a solution to these various problems by means of an electromechanical machine according to claim 1. According to this arrangement, the electromechanical machine benefits, after cooling, from the advantages provided by electrical conductors, in particular windings, superconductors without external means of maintaining the temperature below the critical temperature, benefiting from the mass of the functional part as a heat sink.

It is thus guaranteed by the consideration of the most penalizing mission, with regard to the thermal criteria considered, that the electromechanical machine will remain operational throughout the duration of the mission, whatever the mission carried out for example by the vehicle using this machine.

In this way, the different thermal storage capacities are exploited to obtain optimal thermal autonomy of the mechanical machine with a minimum mass penalty on the machine.

To achieve the objective with the minimum of penalties, in particular mass penalties, the materials entering into the constitution of the functional part are advantageously selected from materials having a high specific heat, greater than 400 J/kg°C and of preferably greater than 800 J/kg°C, so as to form a heat sink capable of accumulating at least a substantial part of the quantity of heat Emax.

Such materials selected according to their specific heats are also selected according to their other requirements (mechanical, electrical, machining, recycling, costs, etc. so as not to penalize the design of the electromechanical machine.

To promote heat exchange, in particular during a cooling phase, the parts made of materials having a high specific heat are arranged and geometrically configured so as to promote heat exchange between these materials and the interior volume of the insulating enclosure. .

A reserve of thermal capacity is thus obtained, the volume of which can be adjusted during the design of the machine, benefiting from the quantity of energy absorbed by the mass of the cryogenic liquid and by the phase change of the cryogenic liquid filling the tank. , when the phase change temperature, from the liquid phase to the gaseous phase, is below the critical temperature, to maintain the temperature in the insulating enclosure below the critical temperature.

In one embodiment, the tank is formed by an internal separator determining, between this internal separator and a more external separator of the insulating wall, the volume of the tank and determining on the side of an internal face a reduced volume in which there is the functional part. According to this arrangement, the functional part is located in a free space in the center of the tank containing the cryogenic liquid, which helps to keep it at low temperature.

To achieve cooling by circulation of cryogenic fluid and filling of the tank with cryogenic fluid, the wall of the insulating enclosure comprises openings for placing the interior volume in communication with the exterior of the insulating enclosure, these openings comprising valves and or valves so as to control the circulation of fluids through said openings.

In order to access the functional part from outside the enclosure in which it is contained, the wall of the insulating enclosure comprises one or more openings through which at least one power transmission shaft passes in a fluid-tight manner mechanism brought to or generated by the functional part so as to have one end of said shaft accessible from outside the insulating enclosure and or comprises one or more openings through which it passes by electrical conductor cables, for example electrical power transmission cables or control and command system cables.

It is thus avoided thermal losses by a circulation of fluid between the interior and the exterior of the enclosure while preserving access to the essential functions of the functional part.

In this case, advantageously, the mechanical transmission shaft(s) and/or the electrical conductors passing through the wall of the insulating enclosure, and in general all the elements such as supports in contact with the interior volume and with the exterior and therefore likely to create thermal bridges unfavorable to maintaining the desired temperature conditions in the interior volume, are made of a material having a thermal conductivity of less than 25 W/m°C.

To carry out the cooling operations and the monitoring of the maintenance of the superconducting operating conditions of the electrical parts of the functional part, the electromechanical machine comprises means for controlling and monitoring the temperature of the interior volume and/or the temperature of the windings made of superconductive material, these control and monitoring means comprising at least one temperature probe fixed to the functional part.

The invention relates in particular to an aircraft comprising such an electromechanical machine. The aircraft then benefits from a reduced mass of the electromechanical machine without new systems being put in place on the aircraft for the production of cold.

In an advantageous form, the invention relates to a vehicle comprising such an electromechanical machine implemented as the propulsion motor of the vehicle.

The invention also relates to a method of operating such an electromechanical machine according to claim 11.

According to one form of the implementation method, a reduced volume of the interior volume of the insulating enclosure in which the functional part is included is filled with cryogenic fluid immersing this functional part as long as the temperature of this functional part is not stabilized at the cryogenic temperature and in which the reduced volume is then purged of the cryogenic fluid which it contains. The cooling of the part providing thermal storage due to its specific heat is thus carried out efficiently and quickly, which proves to be important in the case of successive missions to be carried out by a vehicle carrying the electromechanical machine.

Furthermore, when the electromechanical machine comprises a reservoir inside the insulating enclosure, the reservoir is filled with cryogenic fluid before the disconnection of the external cooling system. The ability to maintain temperature conditions is thus improved.

figure 1 :

une section schématique d'une machine électromécanique suivant l'invention ;

figure 2 :

un schéma bloc du procédé de conception de la machine électromécanique de l'invention ;

figure 3 :

un schéma bloc d'une méthode de mise en froid de la machine de l'invention en vue d'une mission.

The present invention is described with reference to the figures which, in a non-limiting manner, schematically represent:

figure 1 :

a schematic section of an electromechanical machine according to the invention;

picture 2:

a block diagram of the method for designing the electromechanical machine of the invention;

picture 3:

a block diagram of a method of cooling the machine of the invention for a mission.

The various components and elements of the electromechanical machine are not shown to scale.

On the figure 1 accessory elements, supports, electrical cables, sensors, etc. are not shown.

The electromechanical machine 100, schematically illustrated in the figure 1 , comprises a functional part 10 and comprises a thermal control system 20 for regulating a temperature of said functional part.

The functional part 10 performs the functions expected of the electromechanical machine 100, typically the functions of an electric motor and/or those of an electric generator comprising here a rotor 11.

In its general principles and its structure, the functional part 10 conforms to that of known electromechanical machines comprising a moving part, here a rotor 11, and a stator 12. It also comprises, in a known manner, magnetic parts, for example magnets and or parts made of magnetic materials, and comprises at least one electrical conductor, for example a coil made of an electrically conductive material.

In the example shown in the figure 1 , those skilled in the art will recognize a rotating machine, electric motor or generator, comprising stator coils 120 and rotor coils 110.

This example is not limiting, any electromechanical machine comprising coils for the creation of magnetic fields can be implemented within the scope of the present invention.

The electrically conductive materials are, in the case of the electromechanical machine 100, superconductive materials whose electrical resistance becomes zero at a temperature below a critical temperature Tc characteristic of the material used.

The superconducting material is for example a high temperature superconducting material whose critical temperature is greater than or equal to the cryogenic vaporization temperature of a gas (at ordinary temperature) such as liquid diatomic nitrogen, 77 Kelvin at ordinary ambient pressure , such as liquid diatomic hydrogen, 20 Kelvin at ordinary ambient pressure, or such as liquid helium, about 4 Kelvin at ordinary ambient pressure.

In addition, non-electrical parts of the functional part 10, for example a magnetic mass of the rotor 11 or a cage of the stator 12, are made so as to create a thermal accumulation well of a desired capacity, the functions of which will be described later. .

According to this condition, the materials used to produce said non-electrical parts are chosen, within the limits required for their mechanical properties, with specific heats Cp as high as possible.

For example, the non-electrical parts are made by incorporating ferrous materials (Cp of iron = 460 J/Kg °C), aluminum (Cp of aluminum = 890 J/Kg °C), or even boron (Cp = 1300 J/Kg °C) or beryllium Cp = 1800 J/Kg °C).

On the one hand these materials, or other materials having high specific heats, will be preferred to polymeric materials, the use of which is frequent in electric motors and generators, and on the other hand it will be sought to incorporate a sufficient mass of these materials to obtain the desired thermal storage capacity.

Such a result, which will a priori be easier to obtain in the case of electromechanical power machines, and therefore large masses, can also be achieved or approached by incorporating into the interior volume 22 of the insulating enclosure 21 accessories such as reducers or mechanical motion converters which, because of the powers to be transmitted by these reducers or converters, generally represent a mass of materials, capable of carrying out an accumulation of energy in thermal form, not negligible compared to the mass of the electromechanical machine 100.

It follows from these constraints that the architectural criteria and the sizing criteria taken into account by those skilled in the art of designing electromechanical machines are in the present case different from those considered in the ordinary design rules.

The thermal control system 20 mainly comprises an insulating enclosure 21 for thermal insulation of the functional part 10, a device for cooling an interior volume 22 of the insulating enclosure 21 and a system for controlling and monitoring the temperature in said insulating enclosure.

The insulating enclosure 21 is mainly formed by a wall 23 enveloping the interior volume 22.

This wall 23 is made to limit the heat flow between the interior volume 22 of the insulating enclosure, at low temperature, for example at a temperature below 100 Kelvin, and a space outside the insulating enclosure which can be at temperatures around 400 Kelvin, or even more in certain environments.

This type of insulating enclosure is known in particular in the field of cryostats or Deware vessels.

In known manner, the wall 23 most often comprises several separators 230, 231, 232 spaced from each other and delimiting spaces between them. The spaces between the separators determine separation volumes 221, 222.

The outermost separation volume 221, in which a partial gas vacuum is produced and or containing a thermal insulator, for example a silica airgel, provides a first insulation.

Openings 24, 25, 26, 27 of the wall necessarily present in the wall are sealed so as to limit, as much as possible, the exchange of fluid between the interior of the insulating enclosure 21 and the exterior.

Such openings are arranged to provide access to internal parts of said insulating enclosure from the outside of said insulating enclosure.

In the case of the embodiment illustrated in the figure 1 , at least one mechanical power transmission shaft 111, for example integral with rotating parts of the electromechanical machine 100, passes through the insulating wall as well as a bundle of electrical cables.

In one embodiment, not shown, the electromechanical machine does not include a shaft passing through the wall and a mechanical transmission shaft completely outside the insulating enclosure is driven in motion by a magnetic coupling with internal moving parts of the part. functional inside the insulating enclosure.

Preferably, all the elements passing through the wall 23 of the insulating enclosure and the separators 230, 231, 232 are made of materials chosen for their properties as poor thermal conductors.

The concept of materials that are poor thermal conductors is here to be taken in a relative manner insofar as functional criteria, for example the mechanical resistance for a shaft 111 of the electromechanical machine or the electrical conduction for a power cable or a sensor of measurement, must necessarily be taken into consideration.

By way of example, a mechanical shaft is made of a titanium alloy whose thermal conductivity close to 20 W/m°C is lower than that of ordinary steel, having a thermal conductivity at least twice as high, while having a good mechanical resistance, or even an electric cable, at least in its through part of the wall of the insulating enclosure, is made of an iron-nickel alloy with 36% Nickel (such as Invar ^® ) which is also a poor conductor thermal, for a metal, with a thermal conductivity of 13 W/m°C, and whose electrical resistivity, although approximately fifty times that of copper, does not prove to be penalizing over a short length of cable.

Other materials can be used provided that they have similar or better suited characteristics in terms of poor thermal conduction, such as composite materials with a polymer matrix.

The thermal control system 20 also comprises a heat exchanger incorporated into the insulating enclosure.

The concept of heat exchanger is here to be considered in a broad sense. The heat exchanger here incorporates a set of elements and construction characteristics distributed over the electromechanical machine 100 and which promote the transfer of heat between the various elements within said electromechanical machine.

The heat exchanger comprises in particular openings 25, 26 arranged in the wall 23 of the insulating enclosure so as to allow the circulation of a fluid between the interior of said insulating enclosure and the exterior, both in the direction of 'a filling of interior volumes of said insulating enclosure only in the direction of drainage of said volumes. Said openings are provided with shut-off devices 251, 261 controlled, of the valve type, and/or automatic, of the valve type. The passages 25, 26 and the closure devices are arranged to limit the heat exchanges between the interior of the insulating enclosure and the exterior as has already been said, in particular by the use of materials with low thermal conduction. for their accomplishments.

In one embodiment, the heat exchanger implements geometric particularities of the non-electrical parts, made of materials chosen for their thermal accumulation properties, of the functional part 10 which promote heat exchanges inside the enclosure. insulation 21.

Such geometric features consist for example of bores 112, 122 passing through non-electrical parts so that a contact surface of said non-electrical parts with the surrounding fluid is increased to promote heat exchange.

In one embodiment, an internal separator 232 seals the functional part 10 inside a reduced volume 223 of the insulating enclosure 21.

The wall of the internal separator 232 determines, with a separator 231, more external, of the wall 23 of the insulating enclosure, a reservoir 222 enveloping the reduced volume 223 in which the functional part 10 is located. In this case the internal separator 232 does not have any particular thermal insulation characteristic, thermal transparency being sought as much as possible. The internal separator 232 is for example made of aluminum alloy.

In this case, implementing a tank 222, at least one opening 25 for filling and/or draining opens into said tank and said at least one opening, or at least one other opening opening into said tank, is provided with a device regulation, not shown, of the pressure in the tank 222 so as to evacuate a fluid which would be there with a pressure greater than a set pressure.

In this case, according to an embodiment illustrated in the figure 1 , at least one filling and/or drainage opening 26 passes through the volume of the tank 222 and the separators 230, 231, 232 of the insulating wall 23 in a sealed manner so as to open into the reduced volume 223.

The thermal control system 20 also comprises the valves or flaps, the measurement probes and the electrical cables, not shown, necessary or useful for the operation and monitoring of said thermal control system and the temperature of the functional part 10 of the machine. electromechanical 100. As already specified, all wall crossings are sealed and thermally insulated if necessary.

In one embodiment, not shown, the opening opening into the tank 222, and provided with a pressure regulating device, also opens into the reduced volume 223. The cryogenic fluid released by the tank 222 is thus injected into the volume reduced 223 enclosing the functional part 10 which is cooled before said fluid is itself evacuated through an opening 26 of the insulating wall 23 opening into said reduced volume.

The electromechanical machine 100 and its structure, in particular the way in which its structural elements must be designed and produced, will be better understood to the description of the principles implemented during an example of the design, picture 2 , of such an electromechanical machine and the description of the operational implementation, picture 3 , of such an electromechanical machine, which will be described in the context of an electromechanical machine of the electromechanical generator type on board an aircraft.

In addition to the performance conventionally expected of an electromechanical machine intended for a specific use, the person skilled in the art in charge of designing an electromechanical machine implementing the principles of the invention will establish in a first phase 210, depending on the various possible missions for aircraft, the maximum duration of continuous operation of the electromechanical generator.

This maximum duration of continuous operation is in practice the maximum possible duration of a mission of the aircraft, including reserves, which is known, for example 6 hours of mission, and taking into account a safety factor, for example 20% , or 7.2 hours of continuous operation.

Depending on the technologies available to him in the field of superconducting materials, the person skilled in the art will then in a second phase 220 determine the maximum temperature Tmax that the electric generator must not exceed during the maximum duration of the mission with margin, 7.2 hours in the example, to remain functional throughout the mission.

This temperature is for example 75 Kelvin, for a high temperature superconducting material having a critical temperature Tc at least slightly higher than this value.

In a third phase 230, the quantity of energy in thermal form which will be supplied to the electromechanical machine during the previously established duration is determined.

This thermal balance takes into account a heat flow coming from the outside and which comes to heat the functional part 10, heat flow which is a function of the performance of the thermal insulation provided by the insulating enclosure 21, of an outside temperature and of the temperature effectively maintained in said insulating enclosure.

This heat balance also takes into account the heat generated by the functional part 10 inside the insulating enclosure 21. Indeed, although the electrically conductive elements are superconducting under the temperature conditions maintained in said insulating enclosure, the operation of the electromechanical machine 100 dissipates internal energy, in the form of losses in the magnetic parts, of hysteresis, which results in a heat input, which will be determined for the most severe mission profile according to the criterion of said heat input.

It is then deduced from the thermal balance that the electromechanical machine will receive at most an energy Emax (Joule) in the case of the most unfavorable mission.

In a fourth phase 240, given an initial temperature Tmin, for example the temperature of liquid nitrogen at ambient atmospheric pressure on the ground, inside the insulating enclosure 21, and the maximum allowable temperature Tmax , a total static heat capacity CCs (Joule/°C) of the elements inside the insulating enclosure is determined, ie excluding material phase change.

It will be noted that the total static heat capacity CCs is that provided mainly here by the structures of the functional part 10.

Possibly by adapting the static heat capacity CCs by adjustments in the dimensions of the elements of the functional part 10, the electromechanical machine 100 will be able to carry out the mission without its internal temperature exceeding the maximum temperature Tmax, if: $$\mathbf{CCs}\mathbf{x}\left(\mathbf{Tmax}-\mathbf{T\; min}\right)>=\mathbf{Emax}$$

It is then verified in step 250 that this condition is fulfilled or not.

If this condition is fulfilled, the electromechanical machine 100 will a priori only comprise the single mode of keeping cold by a static accumulation of cold, and the essential characteristics of the machine electromechanical are, for the thermal control functions, defined at this phase.

If this condition is not verified, it will be determined in a fifth phase 260 what quantity of a cryogenic liquid must be taken away so as to compensate for the difference between Emax and the term CCs x (Tmax-Tmin) on the one hand by raising the temperature of said cryogenic liquid to a boiling point and on the other hand by changing the liquid phase to the vapor phase of said cryogenic liquid. The cryogenic liquid is in this case necessarily chosen with a boiling point lower than the critical temperature Tc.

In the case of liquid nitrogen, at the atmospheric pressure of 101325 pa, the latent heat of vaporization is about 200 kJ/kg.

The quantity of cryogenic liquid required will in this case determine the volume of the tank 222.

It is obvious that the design cycle which has just been presented in a simplified manner will be carried out by those skilled in the art by a succession of iterations because the thermal dimensioning process is not analytical and requires only intermediate results are repeated with the initial hypotheses to converge towards a final result.

Despite the complexity introduced by the need to maintain the functional part 10 at low temperature, the electromechanical machine 100 proves to be lighter and of smaller dimensions than a conventional electromechanical machine of the same electrical and/or mechanical performance, in particular due to the use of windings made of superconducting materials which allows the passage of currents in the wires of the windings without overheating.

In addition, the thermal control system 20 which maintains conductive elements at cryogenic temperature is completely static.

By applying to the functional part 10 taken as a whole, the thermal control system 20 is much simpler, lighter and more reliable than in the known cryogenic operating systems which seek to cool the parts of electrical conductors.

This result is obtained at the cost of a specific implementation of the electromechanical machine 100.

When the electromechanical machine 100 is to be used, it is cooled beforehand to carry out the mission, for example of the aircraft on which it is installed.

In a first step 310, a source of cryogenic liquid, for example liquid nitrogen at a temperature of 77 Kelvin or less, from an external cooling system is connected to an opening 25, 26 for filling the insulating enclosure, and where applicable, a cryogenic liquid recovery installation is connected to a drainage opening. In the case where the insulating enclosure 21 comprises a reduced volume 223, the openings 26 opening into said reduced volume are connected 320 first.

In a second step 330, cryogenic liquid is sent through the filling opening into the reduced volume 223, or into the interior volume of the insulating enclosure 21 if the latter does not comprise a reduced volume, so as to fill said reduced volume, or said interior volume, and to immerse the functional part 10 which is there. During this second step, the quantity of cryogenic liquid is permanently adjusted if necessary so as to compensate for evaporation of said cryogenic liquid.

It will be noted that in this second step, the geometric shapes chosen for the elements of the functional part 10 used as heat sinks provide an increased contact surface between said elements and the cryogenic liquid, which has the effect of accelerating the temperature of said functional part.

When the temperature of the functional part 10 has dropped and stabilized at the temperature of the cryogenic liquid, which is for example controlled by temperature probes permanently installed in the intermediate enclosure, probes which are connected during this step to the cooling system , the cryogenic liquid is drained 340 outside the enclosure intermediate which is, if necessary, dried without, however, its temperature being raised by this operation.

In a third step 321, when the interior volume 22 of the insulating enclosure 21 comprises a reduced volume 223, which can be carried out simultaneously with step 320, the source of cryogenic liquid, for example liquid nitrogen at the temperature of 77 Kelvin or less, the external cooling system is connected to a filling opening of the insulating enclosure, and if necessary a cryogenic liquid recovery installation is connected to a drainage opening, for the openings 25 leading into the tank 222.

In a fourth step 331 the tank 222 is filled with cryogenic liquid.

Preferably, the external cooling system is kept connected so as to maintain the cryogenic liquid at a desired level for as long as possible, only to be disconnected just before the start of the mission.

It should be noted that the presence of the reservoir 222 enveloping the reduced volume 223, in which the previously or simultaneously cooled functional part 10 is located, ensures that said reduced volume and the functional part 10 are maintained at the temperature of the cryogenic liquid until the start of the mission.

When the external cooling device is disconnected 350, the electromechanical machine 100 becomes independent in terms of controlling its temperature and capable of keeping the internal temperature in the insulating enclosure 21 below the critical temperature Tc for a maximum duration corresponding to the capacity cold storage defined during the design of said electromechanical machine.

As the mission progresses, the heat produced by the functional part 10, minimized by the use of superconductors, and that resulting from the heat flux linked to the temperature difference between the inside and the outside of the insulating enclosure 21 cause, initially increasing the temperature inside the enclosure up to the boiling temperature of the cryogenic liquid, then in a second step the temperature is kept constant at said boiling temperature during an evaporation phase of the liquid cryogenic, finally in a third step the temperature gradually increases from boiling temperature to room temperature. The maximum operating temperature that should not be reached during the mission. The vapors caused by the boiling of the cryogenic liquid are evacuated by the pressure regulating device.

When the mission is finished, the electromechanical machine 100 is again cooled and or the quantity of cryogenic liquid supplemented with a view to a new mission.

Advantageously, when a vehicle, for example an aircraft, comprises a plurality of electric machines of the invention, said vehicle comprises a cryogenic fluid distribution network to which the external cooling device is connected, and centralized monitoring of the temperatures of the different electrical machines connected to this network is also carried out.

It is understood from the examples given of the production, design and use of an electromechanical machine according to the invention that the latter is susceptible to variants while remaining within the general principles of the invention.

In particular, the structure of the insulating enclosure, the shape and layout of a cryogenic tank incorporated in the insulating enclosure, the means for cooling and filling with cryogenic liquid, and the control and monitoring equipment can take various shapes to perform the same functions as those described.

Similarly, the number of cryogenic windings of the functional part, or even the number of independent mechanical parts of the functional part of the same insulating enclosure can be arbitrary.

The person skilled in the art is also able to select materials and parameters such as the type and the temperature of the cryogenic fluid according to the requirements specific to the case in question. Thus the cryogenic fluid can be nitrogen or hydrogen or helium depending on the requirements related to the critical temperature of the superconducting material used.

An electromechanical machine 100 is thus produced which benefits from the advantages of superconducting materials but without being penalized by complex cooling installations thanks to a cold confinement enclosure containing the entire functional part 10 of said electromechanical machine used as a cooling well. heat and the transfer of complex means of cold production to off-board installations.

Such a machine is for example an electric generator whose shaft 111 for driving the moving parts is connected to an external mechanical power source of a propulsion engine or of a gas generator of an auxiliary power unit.

Such a machine is for example an electric motor of an actuator or an electric propulsion motor of a vehicle.

Claims (13)

1. Electromechanical machine (100), comprising at least one part consisting of a winding made of a material that becomes electrically superconductive when its temperature is lower than a critical temperature Tc, a functional part (10) of said electromechanical machine being contained in an internal volume (22) delimited by a wall (23) of a thermally insulating and fluid-tight enclosure (21),

   characterized in that

   the internal volume (22) comprises a tank (222) intended to store cryogenic fluid, in the liquid state when the temperature is lower than the critical temperature Tc, not insulated with respect to the internal volume (22) in terms of thermal conduction, the tank being formed by an internal separator (232) determining, between said internal separator and a more outer separator of the wall (23), a volume of the tank (222), and determining, on the side of an inner face, a smaller volume (223) in which the functional part (10) is located and in that the internal volume (22) comprises:

   - for a temperature range between an initial temperature Tmin, equal to the temperature of a cryogenic fluid and a maximum operating temperature Tmax, at most equal to the critical temperature Tc,

   - a capacity for storing thermal energy in static form and

   - a capacity for storing energy by latent heat from vaporization of a quantity of cryogenic fluid filling the tank (222),

   the capacity for storing thermal energy in static form plus said capacity for storing energy by latent heat from vaporization of the cryogenic fluid representing at least the quantity of heat Emax introduced into said internal volume (22), when the electromechanical machine (100) is used for a duration and in operating conditions corresponding to those of an uninterrupted mission the most detrimental with respect to said quantity of heat out of a set of missions in which said electromechanical machine (100) is likely to be used.
2. Electromechanical machine according to Claim 1, wherein materials involved in the construction of the functional part (10) are selected from among the materials that have a high specific heat, greater than 400 J/kg°C and preferably greater than 800 J/kg°C, so as to form a heat well capable of accumulating at least a substantial part of the quantity of heat Emax.
3. Electromechanical machine according to Claim 2, wherein the materials that have a high specific heat are arranged and geometrically configured so as to promote the heat exchanges between said materials and the internal volume.
4. Electromechanical machine according to Claim 1, wherein the tank is formed by an internal separator (232) determining, between said internal separator and a more outer separator of the wall (23), a volume of the tank (222), and determining, on the side of an inner face, a smaller volume (223) in which the functional part (10) is located.
5. Electromechanical machine according to one of the preceding claims, wherein the wall (23) of the insulating enclosure (21) comprises openings (25, 26) connecting the internal volume (22) with the outside of said insulating enclosure, said openings comprising valves and/or flapgates so as to control the circulation of fluids through said openings.
6. Electromechanical machine according to one of the preceding claims, wherein the wall (23) of the insulating enclosure (21) comprises openings (24, 27) passed through in a fluid-tight manner by at least one mechanical power transmission shaft (111) between the functional part (10) situated in said internal volume (22) and a space outside of said insulating enclosure and/or by electrical conductor cables.
7. Electromechanical machine according to Claim 6, wherein the mechanical transmission shaft or shafts (111) and/or the electrical conductor cables passing through the wall (23) of the insulating enclosure are produced in a material that has a thermal conduction less than 25 W/m°C.
8. Electromechanical machine according to one of the preceding claims, comprising means for controlling and monitoring the temperature of the internal volume (23) and/or the temperature of the windings made of superconductive material, said control and monitoring means comprising at least one temperature probe fixed to the functional part (10).
9. Aircraft comprising an electromechanical machine (100) according to one of the preceding claims.
10. Vehicle comprising an electromechanical machine (100) according to one of the preceding claims, said electrical machine being implemented as a propulsion engine of said vehicle.
11. Method for implementing an electromechanical machine (100) according to one of Claims 1 to 6 comprising a preliminary cooling step and comprising the steps of:

    - connection, when the machine is in a static position, of an external cooling system capable of delivering a liquid at cryogenic temperature lower than the critical temperature Tc at one or more openings passing through the wall (23) of the insulating enclosure (21);

    - filling of at least one volume (223) inside the insulating enclosure (21) containing the functional part (10) of the electromechanical machine (100), with the liquid at cryogenic temperature so as to immerse said functional part;

    - when the temperature of the function part (10) is stabilized at the cryogenic temperature, drainage of the cryogenic liquid from said at least one volume inside the insulating enclosure (21) containing the functional part (10), then disconnection of the external cooling system such that the machine can be operated autonomously in terms of control of its superconductive operating temperature for a maximum duration corresponding to the given mission duration defined during the design of said electromechanical machine.
12. Method according to Claim 11, wherein a smaller volume (223) of the internal volume (22) of the insulating enclosure (21) in which the functional part (10) is included is filled with cryogenic fluid immersing said functional part as long as the temperature of said functional part is not stabilized at the cryogenic temperature and wherein said smaller volume is then purged of the cryogenic fluid that it contains.
13. Method according to Claim 11 or Claim 12, wherein the electromechanical machine (100) comprises a tank (222) inside the insulating enclosure (21), which tank is filled with cryogenic fluid before the disconnection of the external cooling system.

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